High water-absorbent resin composition

ABSTRACT

The present invention is concerned with a high water-absorbent resin composition, produced by forming a composite by fusing or fixing a thermoplastic resin onto a surface of a high water-absorbent resin via an adhesive binder or directly, wherein the composition comprises from 1 to 100 parts by weight of the thermoplastic resin, based on 100 parts by weight of the high water-absorbent resin. 
     When the high water-absorbent resin composition of the present invention is used, it is possible to securely adhere a high water-absorbent resin to a fibrous base material, so that a water-absorbent material which stably retains the high water-absorbent resin even after absorbing water can be obtained. Accordingly, the base materials, such as fibrous base materials, can retain more amount of high water-absorbent resin than those of conventional water-absorbent materials. Thus, it is possible to provide water-absorbent composites suitable for various applications, including hygienic materials, such as paper diapers and sanitary napkins, and agricultural, horticultural, food, and other industrial materials.

TECHNICAL FIELD

The present invention relates to a high water-absorbent resincomposition prepared by forming a composite by fusing or fixing athermoplastic resin onto the surface of a high water-absorbent resin.The high water-absorbent resin composition obtained by the presentinvention has enhanced adhesion. For example, when the highwater-absorbent resin composition of the present invention is used inadhesion to fibrous base materials such as various nonwoven fabrics,pulps or papers, it provides a high water-absorbent material which isnot detached from the fibrous base materials even after which the highwater-absorbent resin absorbs water.

BACKGROUND ART

The high water-absorbent resin is a functional resin capable ofabsorbing and retaining water from several dozens to 1000 times theweight thereof, and because of this property, it is widely utilized inhygienic materials such as paper diapers and sanitary napkins andagricultural and horticultural materials.

However, these high water-absorbent resins are usually in the form ofpowders having no adhesion, and in order to use them in theabove-mentioned applications, the mentioned resin is spread over fibrousbase materials such as nonwoven fabrics, pulps or papers to obtain awater-absorbent material with a sandwich structure. In this case, inorder to fix the high water-absorbent resin to the base material, amethod comprising slightly swelling the resin by water spraying and thensubjecting the swollen resin to embossing or press drying using a rollis normally carried out.

However, the conventional method for fixing the high water-absorbentresin mentioned above has some drawbacks as mentioned below.Specifically, in the method for fixing a high water-absorbent resin to afibrous base material by water spraying, etc., the insufficient adhesionto the base material results in gel detachment upon water absorption, sothat the amount of the high water-absorbent resin to be added for theprevention of the gel detachment is limited. Also, in the case where thewater is used, a drying process becomes necessary for subsequent waterremoval, and at the same time, the touch of the product is affected.

An object of the present invention is to provide a high water-absorbentresin composition having enhanced adhesion to the base material bygiving adhesion to the high water-absorbent resin havingnon-thermoplasticity, which is not detached from the fibrous basematerial mentioned above even after the high water-absorbent resinabsorbs water in the case where it is used in the thermal adhesion tofibrous base materials, such as nonwoven fabrics, pulps or papers.

DISCLOSURE OF THE INVENTION

As a result of intense investigations in view of the above-mentionedcircumstances, the present inventors have found that the desired objectof the present invention can be accomplished by forming a composite byfusing or fixing a thermoplastic resin directly or via an adhesivebinder onto the surface of a high water-absorbent resin, and thus havecompleted the present invention.

Specifically, the gist of the present invention is concerned with:

(1) A high water-absorbent resin composition, produced by forming acomposite by fusing or fixing a thermoplastic resin onto a surface of ahigh water-absorbent resin via an adhesive binder, wherein thecomposition comprises from 1 to 100 parts by weight of the thermoplasticresin and from 1 to 75 parts by weight of the solid component of theadhesive binder, based on 100 parts by weight of the highwater-absorbent resin;

(2) A high water-absorbent resin composition, produced by forming acomposite by fusing or fixing a thermoplastic resin onto a surface of ahigh water-absorbent resin, wherein the composition comprises from 1 to100 parts by weight of the thermoplastic resin, based on 100 parts byweight of the high water-absorbent resin;

(3) The high water-absorbent resin composition mentioned above, whereinthe adhesive binder used is a urethane adhesive;

(4) The high water-absorbent resin composition mentioned above, whereinthe high water-absorbent resin used has an average grain size of from 5to 1000 μm, and the thermoplastic resin is a granular product having anaverage grain size of from 1 to 800 μm, or a fibrous product having anaverage diameter of from 1 to 400 μm and an average length of from 2 to1000 μm;

(5) The high water-absorbent resin composition mentioned above, whereinthe melting point of the thermoplastic resin used is from 50° to 200°C.; and

(6) The high water-absorbent resin composition mentioned above, whereinthe softening point of the thermoplastic resin used is from 40° to 200°C.

BEST MODE FOR CARRYING OUT THE INVENTION

The high water-absorbent resin which can be used in the presentinvention is not particularly subject to limitation, almost allcommercially available products can be used, as long as they havewater-absorbent capacity of from several dozens to 1000 times as much astheir own weights such as those normally used for hygienic materialssuch as paper diapers, sanitary napkins, etc. and agricultural andhorticultural materials. Illustrative examples thereof includecrosslinked acrylate polymers, crosslinked products of vinylalcohol-acrylate copolymers, crosslinked products of polyvinyl alcoholsgrafted with maleic anhydride, cross-linked products ofacrylate-methacrylate copolymers, crosslinked saponification products ofmethyl acrylate-vinyl acetate copolymers, crosslinked products ofstarch-acrylate graft copolymers, crosslinked saponification products ofstarch-acrylonitrile graft copolymers, crosslinked products ofcarboxymethyl cellulose polymers, and crosslinked products ofisobutyrene-maleic anhydride copolymers. These high water-absorbentresins may be used singly or in combination of two or more kinds.

The average grain size of the above high water-absorbent resin which canbe used in the present invention is normally from 5 to 1000 μm,preferably from 20 to 800 μm. For those having finer sizes than 5 μm,its handling becomes difficult, and for those having an average grainsize larger than 1000 μm, uniform dispersion becomes difficult when theobtained high water-absorbent resin composition is spread over a fibrousbase material, so that it would be difficult to obtain a uniform swollenbody after water absorption.

As for the thermoplastic resin used in the present invention, a granularproduct or fibrous product may be used. For thermoplastic resins whichare granular products, the average grain size is normally from 1 to 800μm, preferably from 5 to 500 μm. For thermoplastic resins which arefibrous products, the average diameter is normally from 1 to 400 μm,preferably from 5 to 200 μm and the average length is normally from 2 to1000 μm, preferably from 10 to 800 μm. Also, the thermoplastic resinshaving a melting point of normally from 50° to 200° C., preferably from50° to 170° C., or the thermoplastic resins having a softening point ofnormally from 40° to 200° C., preferably from 40° to 170° C. can beused. When the thermoplastic resins have a melting point of lower than50° C., much care in handling is required, and when they have a meltingpoint exceeding 200° C., a treatment at a higher temperature in thesubsequent adhesion to the fibrous base material is required, making iteconomically disadvantageous. For the same reasons as above, thosehaving a softening point outside the above-mentioned range areundesirable.

The materials for the thermoplastic resins mentioned above are notparticularly subject to limitation, including, for example,ethylene-vinyl acetate copolymers, ethylene-acrylic acid copolymers,ethylene-acrylic ester copolymers, ethylene-acrylic ester-maleicanhydride terpolymers, polyethylene, low-molecular weight polyethylenewaxes, polyesters, polyurethanes, polyamides, polypropylene, and rosinresins, petroleum resins, and terpene resins which are each known astackifier resins, and modified products thereof, which may be usedsingly or in a mixture thereof. Among them, those used in hot meltadhesives, such as ethylene-vinyl acetate copolymers, polyethylene,ethylene-acrylic acid copolymers, polyamides, and polyesters, aresuitably used. These thermoplastic resins may be used singly or incombination of two or more kinds.

The first embodiment of the present invention is a high water-absorbentresin composition characterized by forming a composite by fusing orfixing a thermoplastic resin onto the surface of the above-mentionedhigh water-absorbent resin via an adhesive binder in such a small amountso as not to lower the water-absorption capacity, water-absorption rateand other properties inherent in the high water-absorbent resin.

The methods for obtaining the high water-absorbent resin composition ofthe first embodiment mentioned above are not particularly subject tolimitation. For example,

(1) A method of forming a composite comprising stirring and mixing thehigh water-absorbent resin and the adhesive binder; adding thethermoplastic resin, followed by further stirring and mixing; distillingoff the solvent in the adhesive binder while heating; and then raisingthe temperature to a temperature near the softening point or meltingpoint of the thermoplastic resin or the adhesive binder, and thereby thethermoplastic resin is softened and fused onto the surface of the highwater-absorbent resin; and

(2) A method of forming a composite comprising stirring and mixing thehigh water-absorbent resin and the adhesive binder; adding thethermoplastic resin, followed by further stirring and mixing; distillingoff the solvent in the adhesive binder while heating, and thereby thethermoplastic resin is fixed onto the surface of the highwater-absorbent resin via the adhesive binder may be employed.

In the present specification, "fusing a thermoplastic resin onto asurface of a high water-absorbent resin" means that a thermoplasticresin is adhered onto a surface of a high water-absorbent resin byapplying heat to a thermoplastic resin or adhesive binder to soften andmelt it. Also, "fixing a thermoplastic resin onto a surface of a highwater-absorbent resin" means that a thermoplastic resin is adhered ontoa surface of a high water-absorbent resin by methods other than thosementioned above.

Here, the formulation ratio of the high water-absorbent resin mentionedabove to the thermoplastic resin mentioned above is from 1 to 100 partsby weight, preferably from 5 to 75 parts by weight, of the thermoplasticresin, based on 100 parts by weight of the high water-absorbent resin.This is because when the amount is less than 1 part by weight,sufficient adhesion to the high water-absorbent resin cannot beprovided, and when the amount exceeds 100 parts by weight, no furthereffects are achieved, and rather the water-absorbent performance of thehigh water-absorbent resin is undesirably inhibited. Also, theproportion of the solid component of the adhesive binder used in coatingthe high water-absorbent resin is appropriately from 1 to 75 parts byweight, preferably from 2 to 50 parts by weight, based on 100 parts byweight of the high water-absorbent resin. This is because when theamount is less than 1 part by weight, no corresponding effects areachieved, and when the amount exceeds 75 parts by weight, thewater-absorbent capacity of the high water-absorbent resin isundesirably inhibited.

Examples of the adhesive binders used herein include polyurethane-basedadhesives, such as polyether urethane-epoxy adhesives, polyesterurethane-epoxy adhesives, polyester urethane adhesives, and polyetherurethane adhesives, epoxy adhesives, vinyl chloride adhesives, acrylicadhesives, vinyl acetate adhesives, and synthetic rubber adhesives. Inparticular, favorable results are often obtained in the cases whereurethane-based adhesives, such as polyester urethane adhesives,polyether urethane adhesives or polyether urethane-epoxy adhesives, areused. These adhesive binders may be used singly or in combination of twoor more kinds.

The second embodiment of the present invention is a high water-absorbentresin composition characterized by forming a composite by fusing orfixing a thermoplastic resin directly onto the surface of theabove-mentioned high water-absorbent resin without lowering thewater-absorption capacity, water-absorption rate, etc. inherent in thehigh water-absorbent resin. In this case, it differs from the firstembodiment in that the composite is formed by directly fusing or fixingthe thermoplastic resin without using an adhesive binder.

Methods for obtaining such a high water-absorbent resin composition ofthe second embodiment in which an adhesive binder is not used are notparticularly subject to limitation. For example,

(1) A method of forming a composite comprising raising the temperatureto a temperature near the softening point or the melting point of thethermoplastic resin while mixing and stirring the high water-absorbentresin and the thermoplastic resin, and thereby the thermoplastic resinis softened and fused onto the surface of the high water-absorbentresin; and

(2) A method of forming a composite comprising adding the thermoplasticresin during the production process of the high water-absorbent resin,e.g., at the time of, or after completion of, monomer polymerization;and heating and drying, and thereby the thermoplastic resin is fixedonto the surface of the high water-absorbent resin may be employed.

Here, as in the case of the first embodiment mentioned above, theformulation ratio of the high water-absorbent resin to the thermoplasticresin is from 1 to 100 parts by weight of the thermoplastic resin,preferably from 5 to 75 parts by weight, based on 100 parts by weight ofthe high water-absorbent resin. This is because when the amount is lessthan 1 part by weight, sufficient adhesion to the high water-absorbentresin cannot be provided, and when the amount exceeds 100 parts byweight, no corresponding effects are achieved, and rather thewater-absorbent capacity of the high water-absorbent resin isundesirably inhibited.

The high water-absorbent resin composition of the present invention isapplicable to various base materials to obtain high water-absorbentmaterials. Examples of the base materials include fibrous basematerials, such as nonwoven fabrics, pulps, and papers, which may beprocessed to sheet and other forms. For example, the highwater-absorbent resin composition of the present invention is spreadover fibrous base materials such as nonwoven fabrics, pulps or papers,or alternatively, it is combined with an additional suitable basematerial to give a sandwich structure, followed by thermal adhesion at50° to 200° C. By the above process, the thermoplastic resin grainsfused or fixed onto the surface of the high water-absorbent resin arefused and strongly adhered onto the fibrous base material, so that anexcellent water-absorbent material can be easily obtained, wherein thewater-absorbent gel is not detached from the base material even at thetime of water absorption.

There are two kinds of embodiments, as illustrated by the firstembodiment and the second embodiment as explained above, which areappropriately selected and used depending upon its applications.Although both embodiments show strong adhesion to base materials such asfibrous base materials, the first embodiment using an adhesive binder ispreferably used in applications demanding a stronger adhesion.

The present invention will be explained in further detail below by meansof the following Examples, etc., but the present invention is notlimited to these Examples.

EXAMPLE 1

100 parts by weight of a high water-absorbent resin (trade name: "AQUAKEEP SA-60," based on polyacrylate, average grain size 450 μm,manufactured by Sumitomo Seika Chemicals Co., Ltd.) was placed in abench-type kneader having an inside volume of 1 liter (PNV-IH model:manufactured by Irie Shokai), and 10 parts by weight, calculated as thesolid component of an adhesive binder (a) shown in Table 1, was addedwith stirring, followed by stirring and mixing at room temperature for 5minutes, after which 20 parts by weight of a powdered low-densitypolyethylene (trade name: "FLOTHENE A-1003," average grain size 300 μm,melting point 106° C., manufactured by Sumitomo Seika Chemicals Co.,Ltd.) was added and mixed.

After stirring and mixing for 5 more minutes, the temperature was raisedto 100° C. to distill off the solvent in the adhesive binder to yield ahigh water-absorbent resin composition of the present invention, inwhich the thermoplastic resin was fixed around the high water-absorbentresin and formed as a composite.

                  TABLE I                                                         ______________________________________                                        Ad-                                                                           hesive                                                                        Binder                                                                              Component                                                               ______________________________________                                        <Polyether Urethane-Epoxy Based Adhesives>                                    (a)   ADCOTE 391A     (Main Agent, Solid Comp.:                                                     60%): 100 parts by weight                                                     (manufactured by Toyo                                                         Morton Co., Ltd.)                                             ADCOTE 391B     (Curing Agent, Solid Comp.:                                                   70%): 10 parts by weight                                                      (manufactured by Toyo                                                         Morton Co., Ltd.)                                             Ethanol         24 parts by weight                                      <Polyester-Based Urethane Adhesives>                                          (b)   HI-BON 7031L    (Solid comp.: 20%):                                                           100 parts by weight                                                           (manufactured by Hitachi                                                      Kasei Polymer Co., Ltd.)                                      SUMIDUR L-75    (Curing Agent, Solid Comp.:                                                   75%): 2 parts by weight                                                       (manufactured by Sumitomo                                                     Bayer Urethane Co., Ltd.)                               <Polyurethane-Based Adhesives>                                                (c)   HI-BON 4050     (Solid comp.: 25%):                                                           100 parts by weight                                                           (manufactured by Hitachi                                                      Kasei Polymer Co., Ltd.)                                      DESMODUR R      (Curing Agent, Solid Comp.:                                                   20%): 5 parts by weight                                                       (manufactured by Sumitomo                                                     Bayer Urethane Co., Ltd.)                               <Polyether-Based Urethane Adhesives>                                          (d)   ADCOTE BHS-6020A                                                                              (Main Agent, Solid Comp.:                                                     75%): 100 parts by weight                                                     (manufactured by Toyo                                                         Morton Co., Ltd.)                                             ADCOTE BHS-6020C                                                                              (Curing Agent, Solid Comp.:                                                   35%): 10 parts by weight                                                      (manufactured by Toyo                                                         Morton Co., Ltd.)                                             Ethyl Acetate:  21 parts by weight                                      <Vinyl Acetate Adhesives>                                                     (e)   BOND KE60       (Solid comp.: 50%):                                                           100 parts by weight                                                           (manufactured by Konishi Co.,                                                 Ltd.)                                                   ______________________________________                                    

EXAMPLES 2-5

The high water-absorbent resins and the thermoplastic resins shown inTable 2 and the adhesive binders shown in Table 1 were used to obtainthe high water-absorbent resin compositions of the present invention, inwhich the thermoplastic resins were fused or fixed around the highwater-absorbent resins and formed as composites in the same manner as inExample 1.

EXAMPLE 6

100 parts by weight of a high water-absorbent resin (trade name: "AQUAKEEP 10SH-NF," based on polyacrylate, average grain size 60 μm,manufactured by Sumitomo Seika Chemicals Co., Ltd.) and 10 parts byweight of a spherical ethylene-acrylic acid copolymer (trade name:"FLOBEADS EA-209," average grain size 10 μm, melting point about 90° C.,manufactured by Sumitomo Seika Chemicals Co., Ltd.) were placed in aseparable glass flask having an inside volume of 500 ml, the temperaturewas raised to 100° C. under stirring, and the mixture was kept standingat 100° C. for 15 minutes. The mixture was then allowed to cool understirring to yield a high water-absorbent resin composition of thepresent invention, in which the thermoplastic resin was fused around thehigh water-absorbent resin and formed as a composite.

EXAMPLE 7

A high water-absorbent resin composition, in which the thermoplasticresin was fixed around the high water-absorbent resin and formed as acomposite, was obtained by adding the thermoplastic resin when producingthe high water-absorbent resin by reverse phase suspensionpolymerization. Specifically, 550 ml of n-heptane was placed in a1-liter four-necked cylindrical round bottom flask, equipped with astirrer, a reflux condenser, a dropping funnel, and a nitrogen gas inlettube, and 1.38 g of hexaglyceryl monobehenylate having an HLB value of13.1 (trade name: "NONION GV-106," manufactured by Nippon Oil and FatsCo., Ltd.) was added and dispersed therein. After the dispersion washeated to 50° C. to dissolve the surfactant, the solution was cooled to30° C. Separately, 92 g of an 80% by weight aqueous acrylic acidsolution was placed in a 500 ml Erlenmeyer flask, and 152.6 g of a 20.1%by weight aqueous sodium hydroxide solution was added dropwise whilecooling with ice from outside for a 75 mol % neutralization, after which0.11 g of potassium persulfate was added and dissolved therein. Thispartially neutralized aqueous acrylic acid solution was added to thefour-necked flask and dissolved therein, and the inner atmosphere of thesystem was sufficiently replaced with nitrogen, after which thetemperature was raised, so that the first stage of polymerizationreaction was carried out by keeping a bath temperature at 70° C. Thepolymerization slurry solution was then cooled to 20° C., and 29.4 g ofa low-density polyethylene (trade name: "FLOTHENE UF-80," median grainsize 25 μm, melting point 106° C., manufactured by Sumitomo SeikaChemicals Co., Ltd.) was placed into the system, and the water andn-heptane were distilled off by distillation, followed by drying, toyield 127.4 g of a high water-absorbent resin composition, in which thethermoplastic resin was fixed around the high water-absorbent resin andformed as a composite.

Comparative Example 1

A high water-absorbent resin composition was obtained in the same manneras in Example 1 except that the thermoplastic resin was not added. Sincethe obtained high water-absorbent resin composition was in the form offrom 5 to 6 mm lumps, it was pulverized to from 300 to 500 μm size.

                                      TABLE 2                                     __________________________________________________________________________                         Adhesive                                                 Ex. High Water-Absorbent Resin                                                                     Binder*.sup.)                                                                       Thermoplastic Resin                                __________________________________________________________________________    1   AQUA KEEP SA-60                                                                            100 (a)                                                                             10  Low-Density Polyethylene                                                                     20                                      (Ave. grain size 450 μm)                                                                parts parts                                                                             FLOTHENE A-1003                                                                              parts                                   (manufactured by                                                                           by    by  Ave. grain size: 300 μm                                                                   by                                      Sumitomo Seika Chemicals                                                                   weight                                                                              weight                                                                            Melting Point: 106° C.                                                                weight                                  Co., Ltd.)             (manufactured by                                                              Sumitomo Seika Chemicals                                                      Co., Ltd.)                                         2   AQUA KEEP 10SH-P                                                                           100 (b)                                                                             10  Ethylene-Vinyl Acetate                                                                       30                                      (Ave. grain size 250 μm)                                                                part  parts                                                                             Copolymer      parts                                   (manufactured by                                                                           by    by  FLOVAC D2051   by                                      Sumitomo Seika Chemicals                                                                   weight                                                                              weight                                                                            Ave. grain size: 250 μm                                                                   weight                                  Co., Ltd.)             Softening Point: 56° C.                                                (manufactured by                                                              Sumitomo Seika Chemicals                                                      Co., Ltd.)                                         3   SANWET IM-1000                                                                             100 (c)                                                                             20  Copolymer Polyamide                                                                          50                                      (Ave. grain size 400 μm)                                                                parts part                                                                              AMIRAN 842P    parts                                   (manufactured by                                                                           by    by  Ave. diameter: 50 μm                                                                      by                                      Sanyo Chemical                                                                             weight                                                                              weight                                                                            Length: 500 μm                                                                            weight                                  Industries Ltd.)       Melting Point:                                                                120 to 130° C.                                                         (manufactured by Toray                                                        Industries, Ltd.)                                  4   AQUALIC CA(K Series)                                                                       100 (d)                                                                             50  Polyester      75                                      (Ave. grain size 250 μm)                                                                parts parts                                                                             BYRON GM-900   parts                                   (manufactured by                                                                           by    by  (manufactured by                                                                             by                                      Nippon Shokubai Kagaku                                                                     weight                                                                              weight                                                                            Toyobo Co., Ltd.)                                                                            weight                                  Industries, Ltd.)      Ave. grain size: 75 μm                                                     Melting Point: 113° C.                      5   AQUA KEEP 10SH-NF                                                                          100 (e)                                                                              5  Low-Molecular Weight                                                                         10                                      (Ave. grain size 60,um)                                                                    parts parts                                                                             Polyethylene Wax                                                                             parts                                   (manufactured by                                                                           by    by  AC POLYETHYLENE 1702                                                                         by                                      Sumitomo Seika Chemicals                                                                   weight                                                                              weight                                                                            Ave. grain size: 200 μm                                                                   weight                                  Co., Ltd.)             Softening Point: 85° C.                                                (manufactured by                                                              Allied Signal)                                     6   AQUA KEEP 10SH-NF                                                                          100 --                                                                              --  Spherical Ethylene-                                                                          10                                      (Ave. grain size 60 μm)                                                                 parts     Acrylic Acid Copolymer                                                                       parts                                   (manufactured by                                                                           by        FLOBEADS EA-209                                                                              by                                      Sumitomo Seika Chemical                                                                    weight    Ave. grain size: 10 μm                                                                    weight                                  Co., Ltd.)             Melting Point: 90° C.                                                  (manufactured by                                                              Sumitomo Seika Chemicals                                                      Co., Ltd.)                                         7   Product Obtained by                                                                        100 --                                                                              --  Low-Density Polyethylene                                                                     30                                      Reverse-Phase Suspension                                                                   parts     FLOTHENE UF-80 parts                                   Polymerization                                                                             by        Ave. grain size: 25 μm                                                                    by                                      (Ave. grain size 150 μm)                                                                weight    Melting Point: 106° C.                                                                weight                                                         (manufactured by                                                              Sumitomo Seika Chemicals                                                      Co., Ltd.)                                         Com-                                                                              AQUA KEEP SA-60                                                                            100 --                                                                              --  --             --                                  par.                                                                              (Ave. grain size 450 μm)                                                                part                                                         Ex. (manufactured by                                                                           by                                                           1   Sumitomo Seika Chemicals                                                                   weight                                                           Co., Ltd.)                                                                __________________________________________________________________________     Remarks *.sup.) Calculated as a solid component.                         

Production Example 1

The high water-absorbent resin composition obtained in Example 1 wasspread at 100 g/m² on a pulp sheet (trade name: "Reed Cooking Paper,"manufactured by Honshu Paper Co., Ltd., 100×100 mm, weight: 42 g/m²).After another pulp sheet was covered thereon to provide a sandwichstructure, a water-absorbent material (sheet) was obtained by pressingto adhere onto the entire surface for 5 seconds at a temperature of 130°C. and a pressure of 1 kg/m² using a heat seal tester (Tester SangyoTP-701).

Production Example 2

The high water-absorbent resin composition obtained in Example 2 wasspread at 100 g/m² on one side of a pulp sheet (trade name: "ReedCooking Paper," manufactured by Honshu Paper Co., Ltd., 100×100 mm,weight: 42 g/m²).

Thereafter, a water-absorbent material (sheet) was obtained byheat-treating the mentioned resin composition to adhere onto the pulpsheet for 1 minute at 150° C. using a hot air dryer.

Production Example 3

A water-absorbent material (sheet) made of a pulp sheet was obtained inthe same manner as in Production Example 1 except that the highwater-absorbent resin composition obtained in Example 3 was spread at300 g/m² on a pulp sheet (trade name: "Reed Cooking Paper," manufacturedby Honshu Paper Co., Ltd., 100×100 mm, weight: 42 g/m²).

Production Examples 4-8

Each of water-absorbent materials (sheets) made of pulp sheets wasobtained in the same manner as in Production Example 1 except that thehigh water-absorbent resin compositions obtained in Examples 4-7 andComparative Example 1 were used.

Test Example

The water-absorbent materials (sheets) made of pulp sheets obtained inProduction Examples 1-8 were used to measure the adhesion and the amountof water absorbed by the following method, and to observe the detachmentcondition of the gel at the time of absorbing water.

(1) Measurement method for adhesion strength

A water-absorbent material (sheet) for testing with its edge aloneadhered was prepared in the same manner as in Production Examples exceptthat only the edge of 25 mm width (adhesion area 25×100 mm) were pressedfor adhesion. This sheet was cut into 25 mm wide pieces at a right angleto the longitudinal direction of the adhesion portions to obtain 25×100mm test pieces. The adhesion of the adhesion portion (25×25 mm) wasdetermined using an autograph (AG-500 model, manufactured by ShimadzuCorporation) (peeled at 180 degrees; a peeling speed: 50 mm/min).

(2) Measurement method for the amount of water absorbed

On a 200-mesh standard sieve was placed the water-absorbent material(sheet) obtained in each Production Example, followed by immersion in a0.9% physiological saline for 10 minutes. Thereafter, the sheet wastaken out together with the sieve and excess water was removed, followedby weighing and calculation of the amount of water absorbed as follows:##EQU1## (3) Gel detachment ratio

After the above determination of the amount of water absorbed, thewater-absorbent sheet was taken out from the sieve and weighed (A), andthe ratio of water-absorbent gel which detached from the sheet wascalculated from the weight of water-absorbent gel remaining on the sieve(B) and the weight after water absorption of pulp sheet alone (C):##EQU2##

The results are shown in Table 3.

                  TABLE 3                                                         ______________________________________                                                                           Gel                                        High Water-    Adhesion  Amount of De-                                        Absorbent      Strength  Water     tachment                                   Resin          (g/25 mm  Absorbed  Ratio                                      Composition    width)    (g/m.sup.2)*                                                                            (%)                                        ______________________________________                                        Production                                                                            Example 1  >200      5050    0                                        Example 1          (Breaking                                                                     of Base                                                                       Material)                                                  2       2          --        4800    0                                        3       3          >230                                                                          (Breaking 8700    0                                                           of Base                                                                       Material)                                                  4       4          >250                                                                          (Breaking 3000    0                                                           of Base                                                                       Material)                                                  5       5          >190                                                                          (Breaking 5250    0                                                           of Base                                                                       Material)                                                  6       6          >150                                                                          (Breaking 5540    4.0                                                         of Base                                                                       Material)                                                  7       7          >165                                                                          (Breaking 5100    2.0                                                         of Base                                                                       Material)                                                  8       Comparative                                                                              0         6700    100                                              Example 1                                                             ______________________________________                                         Remarks *.sup.) Amount of water absorbed for the pulp sheet (Reed Cooking     Paper) only was 1200 g/m.sup.2.                                          

The water-absorbent materials using one of the high water-absorbentresin compositions obtained in Examples 1-7 of the present inventionwere found to have a high adhesion and a very low gel detachment ratiowith no significant reduction in the amount of water absorbed, while thewater-absorbent material using the high water-absorbent resincomposition obtained in Comparative Example 1 had no sufficient adhesionso that the entire gel detached from the sheet, though it had a largeamount of water absorbed.

INDUSTRIAL APPLICABILITY

When the high water-absorbent resin composition of the present inventionis used, it is possible to securely adhere a high water-absorbent resinto a fibrous base material merely by thermal adhesion, so that awater-absorbent material which stably retains the high water-absorbentresin even after absorbing water can be obtained. Accordingly, the basematerials, such as fibrous base materials, can retain more amount ofhigh water-absorbent resin than those of conventional water-absorbentmaterials. Thus, when the high water-absorbent resin composition of thepresent invention is used, it is possible to produce water-absorbentcomposites suitable for various applications, including hygienicmaterials, such as paper diapers and sanitary napkins, and agricultural,horticultural, food, and other industrial materials.

We claim:
 1. A high water-absorbent resin composition, produced byforming a composite by fusing or fixing a thermoplastic resin onto asurface of high water-absorbent resin via an adhesive binder, whereinthe composition comprises from 1 to 100 parts by weight of thethermoplastic resin and from 1 to 75 parts by weight of the solidcomponent of the adhesive binder, based on 100 parts by weight of thehigh water-absorbent resin, and wherein said composite is obtained bythe following steps:stirring and mixing the high water-absorbent resinand a solvent containing the adhesive binder; adding the thermoplasticresin, followed by further stirring and mixing; distilling off thesolvent in the adhesive binder while heating; and then raising thetemperature to a temperature sufficient to fuse the thermoplastic resinonto the surface of the high water-absorbent resin but not sufficient tocoalesce the thermoplastic resin.
 2. A high water-absorbent resincomposition, produced by forming a composite by fusing or fixing athermoplastic resin onto a surface of a high water-absorbent resin,wherein the composition comprises from 1 to 100 parts by weight of thethermoplastic resin, based on 100 parts by weight of the highwater-absorbent resin, and wherein said composite is obtained by thefollowing step:raising the temperature, while mixing and stirring thehigh water-absorbent resin and the thermoplastic resin, to a temperaturesufficient to fuse the thermoplastic resin onto the surface of the highwater-absorbent resin but not sufficient to coalesce the thermoplasticresin.
 3. The high water-absorbent resin composition according to claim1, wherein the adhesive binder is a urethane adhesive.
 4. The highwater-absorbent resin composition according to claim 1 or 2, wherein thehigh water-absorbent resin has an average grain size of from 5 to 1000μm, and the thermoplastic resin is a granular product having an averagegrain size of from 1 to 800 μm, or a fibrous product having an averagediameter of from 1 to 400 μm and an average length of from 2 to 1000 μm.5. The high water-absorbent resin composition according to claim 1 or 2,the thermoplastic resin has a melting point of from 50° to 200° C.
 6. Ahigh water-absorbent resin composition, produced by forming a compositeby fixing a thermoplastic resin in the form of grains onto a surface ofa high water-absorbent resin via an adhesive binder, wherein thecomposition comprises from 1 to 100 parts by weight of the thermoplasticresin and from 1 to 75 parts by weight of the solid component of theadhesive binder, based on 100 parts by weight of the highwater-absorbent resin, and wherein said composite is obtained by thefollowing steps:stirring and mixing the high water-absorbent resin and asolvent containing the adhesive binder; adding the thermoplastic resin,followed by further stirring and mixing; and distilling off the solventin the adhseive binder while heating, and thereby fixing the grains ofthermoplastic resin onto the surface of the high water-absorbent resinvia the adhesive binder.
 7. A high water-absorbent resin composition,produced by forming a composite by fixing a thermoplastic resin in theform of grains onto a surface of a high water-absorbent resin, whereinthe composition comprises from 1 to 100 parts by weight of thethermoplastic resin, based on 100 parts by weight of the highwater-absorbent resin, and wherein said composite is obtained by thefollowing steps:adding the thermoplastic resin during a productionprocess of the high water-absorbent resin; and heating and drying, andthereby fixing the grains of thermoplastic resin onto the surface of thehigh water-absorbent resin.
 8. A composition, comprising a highwater-absorbent resin having grains of a thermoplastic resin fused orfixed to a surface thereof, wherein said grains of thermoplastic resindo not coalesce together and are fused or fixed in such a small amountthat the water absorption capacity and water absorption rate of saidwater-absorbent resin is not substantially reduced, and wherein saidcomposition comprises from 1 to 100 parts by weight of the thermoplasticresin per 100 parts by weight of the high water-absorbent resin.
 9. Thecomposition according to claim 8, wherein said thermoplastic resin isfused or fixed to the surface of the high water-absorbent resin via anadhesive binder, which is contained in an amount of from 1 to 75 partsby weight of the solid component therein per 100 parts by weight of thehigh water-absorbent resin.
 10. The composition according to claim 8,wherein said water-absorbent resin is selected from the group consistingof crosslinked acrylate polymers, crosslinked products of vinylalcohol-acrylate copolymers, crosslinked products of polyvinyl alcoholsgrafted with maleic anhydride, crosslinked products ofacrylate-methacrylate copolymers, crosslinked saponification products ofmethyl acrylate-vinyl acetate copolymers, crosslinked products ofstarch-acrylate graft copolymers, crosslinked saponification products ofstarch-acrylonitrile graft copolymers, crosslinked products ofcarboxymethyl cellulose polymers, and crosslinked products ofisobutyrene-maleic anhydride copolymers.
 11. The composition accordingto claim 10, wherein said thermoplastic resin is selected from the groupconsisting of ethylene-vinyl acetate copolymers, ethylene-acrylic acidcopolymers, ethylene-acrylic ester copolymers, ethylene-acrylicester-maleic anhydride terpolymers, polyethylene, low-molecular weightpolyethylene waxes, polyesters, polyurethanes, polyamides, andpolypropylene.